Phenolic molding composition



Pat nt uli 5.19.44:

z'ssmisi rnmmemmmd ooiurosrnoiv Frits kesenthalfKnoxville, Tenn.,assignm'v .The University of Tennessee Research Corporation, Knonville,Tenn., a corporation of Ten;

NoDrawing. smalls-1; April 19,1941;

Serial No."389,466

. 4 Claims. This invention 'pertain s to an improved "mold:

ing composition,cif rnpounded of synthetic.- resins and a fillerconsisting of comminuted'leather,

which will assume a hardand infuslble form'when subiectedlto heat andpressure. j 1

Leather and phen -aldehyde resins have been compounded inthe ;art t oformginolding compositions. modify the protein of which the leather islargely composed prior to itsincorporation with .the

phenolic re'sinQ 'I'he leather protein is of exceedingly complex nature.;In the past a. compounding ofthispl'jq ein with resin has been possibleonly after the submission, he protein to" a partial degradation orhydrolysis; Usually; the.

hydrolysis was carried out simultaneously with, the initialcondensationjof the phenol and the formaldehyde" This hydrolysis of theleather.

protein hadqcertain unfortunate manifestations in the final product;,The degradation or weakening of the protein molecule resulting from itsIt has been necessary, however, to.

. suresapplied perpendicularly tothe leather sur-. face, a separatingor. breaking downbetween hydrolysis tended to decrease the strength 'ofl the "leather fibers and resulted in a substantial weakening of thefinal product. Moreover this hydrolysis converted the leather fiber froman ideal filler of great elasticity, tensile strength and toughness toan inferior mass of deteriorated fibers.

The primary object of the present invention, therefore, is to evolve apreliminary processing of the leather fibers which will not reduce theirstrength or result in their chemical deterioration and which will atthesame time place them in such condition as to be readily compounded withphenol-aldehyde condensation products. A treatment of the leather fiberswhich will preserve their chemical and physical characteristics andmaintain them with their inherent toughness and mechanical strengthintact, allows a highly superior molding composition to be produced.For, this reason a mechanical, rather than a chemical, preparation ofthe fibers has been evolved.

The processing of leather scrap involves two steps. reduced to desirableparticle shape and size to suitably increase the impregnating surface ofthe leather. Secondly, the fats and oily materials added to the leatherfor the purposes of softening and tanning must be removed.

In the past thehydrolysis step has been found First, the fibers must beseparated and necessary to soften, separate and cleanse the fibers toplace'them in condition for compounding with the phenolic resin. It hasnot been considered possible to prepare the fibers by 7 mill type.

merely mechanical means as it is. impossible, due

to their toughness, properly to prepare themby grinding in aconventional mill of the hammer I have discovered that when the leatherscrap is first submitted tointense pres-' the fibers .resultswhichenables ,them. subsequently to becomminuted satisfactorily, inthe hammermill. This perpendicular pressing may be .-accomplished satisfactorilyby passing the leather through a system 'of pressure rollers of. smallclearance.- This step has a flaking and.

squeeaingaction on theleather which loosens the bond between the leatherfibers without having a deteriorating eflect onithe fibers. Subsequenttothe pressing step a homogeneous fibrous mass. mayreadilybe produced bypassing theprepared leather through a-hammer mill.

The second; step involves the removalof the tanning fatsand oils addedtothe leather in processing. 'The presence of these fats and oils tendsto inhibit a proper cure of the phenolic resin when the molding compoundis submitted to heat and pressure. The removal of these fats and oils isreadily accomplished by the use of an organic solvent. After the leatheris reduced to a fibrous mass of decreased particle size, properpenetration of the solvent is greatly facilitated. It has beendetermined that two washings with petroleum ether or other organicsolvents will reduce the fatty content from 20% to .5%. The smallresidual percentage of oil has no deleterious efiect on the curing ofthe phenolic resin. As a matter of fact it acts as a lubricant whichprevents sticking of the compound in the mold and obviates the use ofthe conventional lubricants usually used with molding compounds forthispurpose. The oil recovered by solvent extraction may be reused intanneries for the further processingof other leathers and contributes tothe economy of this process.

' One molding composition prepared according to this process is asfollows:

150 grams-of phenol, 240 grams of a-40% aqueous solution offormaldehyde, and 1.5 grams of sodium hydroxide dissolved in 15 cc. ofwater,

are refluxed for 45 minutes in a glycerin bath of' C. The resultingresin syrup is mixed in a dough mixer with 300 grams of comminutedextracted leather and 7.5 grams of lime. The mixed compound is dried forten hours in a Gordon drier at 55 C. This compound, when subjected totemperatures of from 280-360 F. and pressures of from 2000-4500 poundsper 2 asses-1o I square inch in a suitable mold, will produce aninfusible molded object of superior impact strength and toughness.

In the composition disclosed approximately 38% of phenolic resin isutilized with the fibers.

This percentage of resin may be increased or decreased and theprocedure'may be modified in various ways known to the art as wetmix anddry mix processes. By varying the percentage of resin to leatherthecharacteristics oi the plastic material may be modified within wideranges. I'urther, if desired, certain other filler materials of knownproperties may be incorporated with the leather fiber to modify thecharacteristics 1 of the molding composition.

As indicated above, the invention is susceptible of numerousmodifications and embodiments. The foregoing formula is by way ofillustration only and nothing in the specification is intended to limitthe scope of the invention. Attention is directed to the appended claimsfor this purpose.

What is claimed is:

l. The method of forming a molding composition comprising a syntheticresin and a leather filler which consists in subjecting leather scrap toa pressure sufilcient to break the bond between the fibers and separatethe leather intov individual fibers with their natural chemical andphysical properties unimpaired, then comminuting the fibers to a desiredparticle size to facilitate removal of thecontained oils and fats andincrease their resin-irnpregnatlng surfaces, then subjecting thecomminuted fibers to an organic solvent to remove substantially allofthe contained oils and fats, then adding thereto a phenolic-formaldehyderesin syrup and then drying the mixture.

2. The method of forming a molding composition comprising a syntheticresin and a leather to a pressure sufilcient to break the bond befillerwhich consists in subjecting leather scrap to a pressure sumcient tobreak the bond between the fibers and separate the leather intoinditween the fibers and separate the leather into individual fiberswith their natural chemical and physical properties unimpaired, thencomminuting the'fibers to a desired particle size to facilitate removalof the contained oils and tats and increase-their resin-impregnatingsurfaces,

thensub'lecting the comminuted fibers to an organic solvent to removesubstantially all of the contained oils and fats, then adding thereto aphenolic-formaldehyde resin syrup in an amount equal approximately to40% of the mixture and then drying the mixture.

4. The method of forming a molding composition comprising a syntheticresin and a leather filler which consists in subjecting leather scrap toa pressure sufiicient to break the bond between the fibers and separatethe leather into individual fibers with their natural "chemical andphysical properties unimpaired, then comminuting the fibers to a desiredparticle size tofacilitateremoval of the contained oils and fats andincrease their resin-impregnating surfaces, then subjecting thecomminuted fibers to an organic solvent to'remove substantially all ofthe contained oils and fats, then adding thereto a phenolic-formaldehyderesin syrup in an amount equal approximately to 40% of the mixture andthen dryin the mixture at approximately 55 C.

